Imaging device and method of manufacture

ABSTRACT

An imaging chip is packaged in transparent injection molded material. The chip may have photosensitive elements arranged in a two-dimensional array on semiconductor material. Each element corresponds to a pixel of an image. The package may be formed of epoxy resin. In one aspect of the invention, the transparent plastic material provides a color filter. Second and third packages with complementary color filters may be used to provide signals for a color imaging system. In another aspect of the invention, a lens is integrated into the plastic package. In another aspect of the invention, a semiconductor chip is applied to a pre-formed plastic package by bump bonding.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to imaging devices. Theinvention also relates to methods of packaging such devices. Moreparticularly, the invention relates to a transparent plastic package forsupporting and/or protecting a photosensitive semiconductor device.

2. Discussion of the Related Art

Solid-state imaging devices are known in the art. They are used togenerate electrical signals representative of an incident image. Thedevices may be responsive to visible, ultraviolet and/or infraredradiation. The devices may also be used to generate color componentsignals. Solid-state imaging devices are described in U.S. Pat. Nos.5,708,263 (Wong), 5,461,425 (Fowler et al.) and 4,441,125 (Parkinson).

Prior art imaging devices are packaged in ceramic and glass platestructures. Such packages are generally cumbersome and inconvenient, andthe materials are relatively expensive. In addition, the known packagesrequire complicated methods of assembly. A ceramic housing must first beproduced. The ceramic housing is used to provide support for the glassplate. The housing must be carefully constructed to ensure properalignment of the imaging device and the glass plate. Then, the imagingdevice is secured within the ceramic housing. The imaging device needsto be properly aligned in the housing to avoid misalignment with theplate, which could cause optical distortion. And before the glass plateis applied, steps must be taken to provide electrical communication fromthe leads of the imaging device to the exterior of the solid ceramichousing.

Then, the glass plate is applied and it is necessary to permanentlysecure the plate to the housing. The connection between the glass plateand the housing must be permanent and air tight. In addition, thereshould be no misalignment of or damage to the plate. All of these stepsmust be done in a contaminant-free environment. Dust or othercontaminants on the imaging device or inside the glass plate coulddegrade the performance of the device. The various steps may requiredifferent machinery. Consequently, it may be necessary to move partiallyassembled parts from one machine to another.

There is a need in the art for imaging devices that are constructed oflow-cost materials. There is also a need in the art for an uncomplicatedmethod of packaging imaging devices. There is also a need in the art fora packaging system that is readily adaptable to existing machinery andskills in the semiconductor device manufacturing industry.

SUMMARY OF THE INVENTION

The disadvantages of the prior art are overcome to a great extent bypackaging an imaging chip in transparent plastic material. The chip mayhave photosensitive elements located on semiconductor material. Thepackage may be formed of relatively inexpensive injection molded resin.In one aspect of the invention, the resin is a thermosetting epoxyresin. In another aspect of the invention, the photosensitive elementsare arranged in a two-dimensional array. Each element corresponds to apixel of an image.

In another aspect of the invention, the transparent plastic materialprovides a color filter. Second and third packages with complementarycolor filters may be used to provide complementary signals in a colorimaging system.

The present invention also relates to an imaging device that has apackage formed of transparent plastic material and a semiconductor chiplocated within the package. The chip has an array of photosensitiveelements for generating electrical signals corresponding to an image.The photosensitive elements are covered by the transparent plasticmaterial.

In one aspect of the invention, a lens is incorporated into the plasticpackage. The lens transmits the image onto the photosensitive elements.The lens may be formed by injection molding.

The present invention also relates to a system that has an image sourcefor transmitting an image, a semiconductor device for responding to theimage, and a package for protecting and supporting the semiconductordevice. The package is formed of injection molded transparent plasticmaterial. The image is transmitted through the plastic material.

The present invention also relates to a method of making a packagedimaging device. The method includes the following steps: locating anintegrated circuit in a mold; injecting transparent resin into the moldsuch that the integrated circuit is covered by the resin; curing theresin; and removing the finished product from the mold. In one aspect ofthe invention, a release agent is applied to the mold for easy removalof the finished product.

In another aspect of the invention, a semiconductor chip is applied to apre-formed plastic package by bump bonding. The package may be formed ofinjection molded transparent plastic.

These and other features and advantages of the invention will becomeapparent from the following detailed description of preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a isometric view of an imaging device constructed inaccordance with the present invention.

FIG. 2 is a top view of another imaging device constructed in accordancewith the invention, at an intermediate stage of manufacture.

FIG. 3 is a cross-sectional view of an imaging system constructed inaccordance with the invention.

FIG. 4 is a cross-sectional view of another imaging device constructedin accordance with the invention.

FIG. 5 is a schematic view of another imaging system constructed inaccordance with the invention.

FIG. 6 is a cross-sectional view of another imaging system constructedin accordance with the invention.

FIG. 7 is a cross-sectional view of yet another imaging deviceconstructed in accordance with the invention.

FIG. 8 is a bottom view of yet another imaging device constructed inaccordance with the invention.

FIG. 9 is a top view of the imager chip for the device of FIG. 8.

FIG. 10 is a top view of the package for the device of FIG. 8.

FIG. 11 is a top view of yet another imaging device constructed inaccordance with the invention.

FIG. 12 is a cross-sectional view of the imaging device of FIG. 10,taken along the line 12-12.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, where like reference numerals designatelike elements, there is shown in FIG. 1 an imaging device 10 constructedin accordance with the present invention. The device 10 has asemiconductor chip 12 and metal leads 14. The inner ends 16 of the leads14 are connected to the chip 12 by suitable lead wires. The lead wiresare not shown in FIG. 1.

The chip 12, the lead wires, and the inner ends 16 of the leads 14 arecompletely encapsulated in a transparent plastic package 18. The package18 provides structural support for the chip 12, the lead wires and theleads 14. In addition, the package 18 protects the chip 12 from theenvironment. Other features and advantages of the transparent package 18are described in more detail below.

The chip 12 may be formed of semiconductor material. The chip 12 may be,for example, a complementary metal oxide semiconductor (CMOS) device.The chip 12 has photosensitive elements 20 for receiving radiant energyfrom an image source and for generating corresponding electricalsignals. The photosensitive elements 20 are covered by the transparentpackage 18. Suitable circuitry (not illustrated) may also be integratedinto the chip 12.

The photosensitive elements 20 may be in a suitable two-dimensionalarray. For example, the elements 20 may be arranged in a 480×640 array.The invention should not be limited, however, to the number orparticular arrangement of photosensitive elements 20 on the chip 12.More or less elements 20 may be used to practice the invention.

The photosensitive elements 20 generate pixel signals representative ofthe radiant image that is incident on the surface of the chip 12. Thesignals are transmitted through the wires and the leads 14, andprocessed to reconstruct a version of the image at a remote location.Thus, the imaging device 10 may be used, for example, in a digitalelectronic camera. The invention should not be limited, however, to anyparticular field of use. The invention may be used in a wide variety ofradiation sensing systems, image processing systems and other systems.

In the illustrated embodiment, the package 18 is formed of a clear epoxyresin. Other thermosetting resins, or other plastic materials, includingthermoplastic resins, may be used if desired. The coefficient ofexpansion for the plastic material may be substantially different thanthat of the chip 12.

The device 10 may be economically manufactured by injection molding. Inoperation, the chip 12, the wires (not shown in FIG. 1) and the leads 14are assembled and located in a suitable mold (not illustrated). Epoxyresin is injected into the mold to completely and integrally surroundthe chip 12, the wires and the inner ends 16 of the leads 14. The epoxyresin is then cured to form the rigid, self-supporting package 18. Notethat the wires between the chip 12 and the leads 14 are not shown inFIG. 1 in order to better show the manner in which the chip 12 isencased in transparent plastic material.

Preferably, the injection molding process is controlled to maintain thetransparency of the plastic material over the photo-sensitive elements20. For example, the formation of bubbles in the plastic material nearthe photosensitive elements 20 should preferably be avoided. Suchbubbles may affect the resolution of the imaging device 10. For certainuses, however, where high resolution is not required, small bubbles andother imperfections in the molded plastic package 18 may be tolerated.

FIG. 2 shows another imaging device 30 constructed in accordance withthe invention. The device 30 is formed by injection molding the package18 on a lead frame 32. The lead frame 32 has a paddle 34 for supportingthe chip 12. Lead frames of the type shown in FIG. 2 are disclosed forexample in U.S. Pat. No. 5,021,864 (Kelly).

To manufacture the device 30, the chip 12 is adhesively attached to thepaddle 34. Wires from pads on the chip 12 are bonded to the respectiveleads 14 on the lead frame 32. The assembly 12, 32 is then located in amold (not illustrated). Clear epoxy is injected into the mold and curedto form the package 18. The lead frame 32 is then trimmed away at theouter ends of the leads 14 to produce the finished product.

Preferably, the transparent molded material completely surrounds the topsurface of the chip 12, the bottom surface of the paddle 34, and theinner ends 16 of the leads 14. The plastic material may fill the spacesbetween the inner ends 16 of the leads 14 to provide a rugged,integrated assembly. The advantages, features and uses of the imagingdevice 10 shown in FIG. 1 are applicable to the imaging device 30 shownin FIG. 2.

As shown in FIG. 3, the imaging device 10 may be assembled adjacent alens 40 to provide an imaging system 42. A suitable support structure 44may be provided to support the imaging device 10 and the lens 40. Thelens 40 provides an image source for the system 42. In operation,radiation 46 incident on the lens 40 is imaged on the surface of thechip 12. The photosensitive elements generate pixel signalsrepresentative of the image. The signals are transmitted through leadwires 48 and signal wires 50 for processing.

Referring now to FIG. 4, a lens 52 may be molded into a plastic package54. The lens 52 may be formed during the injection molding of thepackage 54, as a single step operation. The package 54 is the same asthe package 18 shown in FIG. 1 except for the integrally molded lens 52.The lens 52 may be used instead of or as a complement to the lens 40 ofFIG. 3.

FIG. 5 shows a color imaging system 60. The system 60 has a beamsplitter 62 and first, second and third component imaging devices 64,66, 68. The beam splitter 62 transmits the same image onto each of thecomponent imaging devices 64, 66, 68. The split beams of radiation aredesignated by arrows 70, 72, 74. The component imaging devices 64, 66,68 may be identical to the imaging devices 10, 30 discussed above,except that the molded packages 18R, 18G, 18B for the devices 64, 66, 68are formed of red, green and blue transparent plastic, respectively. Thecolored packages 18R, 18G, 18B provide respective color componentfilters.

Thus, the chip 12 for the first component imaging device 64 receivesonly the red component of the image from the beam splitter 62. The chips12 for the second and third imaging devices 66, 68 receive only greenand blue components of the image, respectively. Signals from the threeimaging devices 64, 66, 68 may be combined via signal lines 76, 78, 80to produce a color version of the image at a remote location 82.

The component imaging devices 64, 66, 68 shown in FIG. 5 may be providedwith integrally molded lenses 52 of the type shown in FIG. 4. Thedevices 64, 66, 68 may also be used with a separate lens 40 of the typeshown in FIG. 3. In each case, the devices 64, 66, 68 may be molded withor without a paddle lead frame 32.

In an alternative embodiment of the invention, the red, green and bluecolor filters integrated into the packages 18 may be replaced bysubtractive cyan, magenta and yellow transparent packages. Thetransparent plastic for the packages may be colored with a variety ofdifferent colors depending on the parameters of the system within whichthe imaging devices are used.

In an alternative embodiment of the invention, a single imaging device10 may be associated with a color filter array (CFA) 84 (FIG. 6). Anexample of a color filter array is shown in U.S. Pat. No. 5,668,596(Vogel). The color filter array 84 may provide a separate color filter(red, green or blue) for each pixel of the image. The individual filterson the color filter array 84 are aligned with the photosensitiveelements 20 on the chip 12 such that the single chip may be used forcolor image processing. In the embodiment shown in FIG. 6, the plasticmaterial making up the package 18 is clear (with no color).

Referring now to FIG. 7, in another embodiment of the invention, thecolor filter array 84 may be located within and entirely surrounded bythe plastic material of the package 18. As in the embodiment of FIG. 6,the individual filters of the color filter array 84 are aligned with therespective photosensitive elements 20 on the chip 12 for colorprocessing.

Referring now to FIGS. 8-10, another imaging device 90 constructed inaccordance with the invention is formed by bump bonding a semiconductorchip 92 onto a pre-molded plastic package 94. FIG. 9 shows the chip 92by itself, before the chip 92 is bonded to the package 94. The chip 92generally has the features and advantages of the chip 12 discussedabove. In addition, the chip 92 has bond pads 96. The pre-molded package94 is shown in FIG. 10. The package 94 may be formed of the transparentepoxy material discussed above. In addition, the package 94 has bondpads 98 for providing electrical connections to respective metal leads14. The preferred method of making the imaging device 90 is described inmore detail below.

To manufacture the imaging device 90, the leads 14 and the bond pads 98for the package 94 are assembled in a mold (not illustrated).Transparent epoxy resin (or another moldable material) is injected intothe mold. The plastic material is cured to form a structure that rigidlysupports the leads 14 and the bond pads 98. The chip 92 is then flippedand bump bonded onto the pads 98. The pads 96 on the chip 92 aresoldered to the pads 98 on the package 94 to establish electricalconnections between the photosensitive elements 20 and the leads 14. Ifdesired, a suitable resin may be applied to the back surface of the chip92 to complete the device 90.

In an alternative embodiment of the invention, the package 94 may becolored for use in a color imaging system of the type shown in FIG. 5.The packages 94 may be formed with or without integral lenses 52 of thetype shown in FIG. 4.

Referring now to FIGS. 11 and 12, another imaging device 110 constructedin accordance with the present invention includes a housing 112, a chip12, and a molded transparent plastic cover 114. The photosensitiveelements 20 are connected to suitable leads 14 on the chip 12.

To manufacture the device 110, the rigid housing 112 may be made ofceramic or molded plastic. The chip 12 is then located in the housing112 and connected to the leads 14. The cover 114 may then be formed byinjecting molten epoxy resin (or another suitable plastic material) intothe housing 112. The molten material encapsulates the chip 12 and theleads 14.

The molten material may be conveniently contained within the housing 112during the molding process by the side walls 116 of the housing 112. Thehousing 112 has a closed bottom 118 to prevent molten plastic fromdraining out of the housing 112 by gravity. Thus, the housing 112 servesas a mold during the formation of the cover 114.

The molten plastic material is cured or hardened to produce a rugged,integrated final product. The solid plastic material 114 secures thechip 12 in place within the housing 112 and protects the chip 12 fromthe environment.

The cover 114 may be clear or colored, as in the embodiments discussedabove. A lens 52 may be molded into the cover 114, if desired. A colorfilter array 84 of the type shown in FIG. 7 may be molded into the cover114, if desired.

The above descriptions and drawings are only illustrative of preferredembodiments which achieve the features and advantages of the presentinvention, and it is not intended that the present invention be limitedthereto. Any modification of the present invention which comes withinthe spirit and scope of the following claims is considered part of thepresent invention.

1-31. (canceled)
 32. A method of making an image device, comprising thesteps of: locating a semiconductor device in a mold, said deviceincluding an integrated circuit and photosensitive elements; attachingleads to said semiconductor device; locating a color filter array insaid mold; injecting a transparent thermosetting resin into said moldsuch that said integrated circuit and said photosensitive elements arecovered by said transparent resin; curing said thermosetting resin toform a package encapsulating said semiconductor device, said packageproviding a color filter in said transparent resin.
 33. A method ofmaking an image device, comprising the steps of: locating asemiconductor device in a mold, said device including an integratedcircuit and photosensitive elements; locating a color filter array insaid mold; injecting transparent resin into said mold such that saidintegrated circuit, said photosensitive elements, and said color filterarray are covered by said transparent resin; and subsequently, removingsaid semiconductor device from said mold.
 34. The method of claim 33,further comprising the steps of attaching leads to said semiconductordevice, said leads being partially encapsulated in said transparentresin.
 35. The method of claim 34, wherein said transparent resin is athermosetting resin, and further comprising the step of curing saidthermosetting resin to form a package encapsulating said semiconductordevice.
 36. The method of claim 35, further comprising the step offorming a lens in said package.